1. Field of the Invention
The present invention relates to the field of photonic applications. In particular, the present invention relates to a method and system for controlling the phase of electromagnetic signals.
2. Description of the Related Technology
A variety of photonic applications use photodetectors in analog systems, such as basic optical microwave links, phased arrays and photonic analog-to-digital converters. In these systems, microwave signals are modulated onto optical carriers, transmitted and subsequently received by photodetectors to recover the amplitude and phase. The phase of the microwave signal is influenced by system and environmental parameters, such as path length and dispersion. For example, external compensation for the factors that influence the microwave phase is often accomplished via microwave phase shifters. When using high frequency (20-100 GHz) microwaves, microwave phase shifters produce less than ideal results. Microwave phase shifters also fail to continuously change the phase of the microwave signal.
Analog optical systems with a continuously tunable microwave phase are needed for a wide variety of applications, from photonic analog-to-digital converters to optical microwave links and phased arrays. In order to achieve a large dynamic range, photodetectors with high-saturation currents are necessary. In the 1550-nm wavelength region, wide-bandwidth, InGaAs photodetectors with high photocurrents are made using several designs, among them: dual depletion, uni-traveling carrier, and partially depleted absorber (PDA) photodetectors. Additionally, integrating photodiodes with waveguides (waveguide photodetectors) have shown progress in increasing the photocurrent while maintaining a wide bandwidth.
In each of the above discussed designs, high optical fluence eventually causes nonlinear behavior in the photodetector which ultimately leads to saturation. The leading nonlinear mechanisms include carrier screening of the electric field in the depletion region and band filling. These mechanisms manifest themselves in the photodetector's response by broadening the time response of the resulting electrical waveforms and reducing the photodetector's responsiveness, respectively. To achieve the desired dynamic range over the bandwidth of interest, the detected optical signal must be large enough to provide the necessary signal-to-noise ratio, but must also remain below the saturation level.
Therefore, there is a need in the field to provide an improved method and system for dynamically changing the phase of the microwave signal.